First feedback - discussion thread

[ronnybremer]

Thank you for all your work @Gmin2! I really appreciate the way this crate interacts easily with the local CUPS system. Makes life a lot easier if you don't have to do IPP coding directly.

During the integration in my current project I have found a few things I will need to work on. Maybe its something I could add to this crate as a PR:

• querying the printer for available input slots
• easy way to specify the input slot to use when submitting a job
• should we still use the job option media or should we use PageSize when creating a print job? I have found lots of information on both but I am not sure if media is outdated with CUPS v2.
• the crate allows for easy media query from the printer, however, they are only returned in inches, maybe allow for a conversion to pt and mm
• easy way to specify margins for print jobs, currently it requires custom_option
• allow to override the requesting user. Right now the currently logged in user is used as the owner of the print job, however, in a Kiosk setup different users might sign into the app and the print job should reflect that.
• somehow build an async wrapper. As everything with CUPS printing can take a long time from start to finish one needs to be mindful when using the crate in an asynchronous environment (as you also clearly mention in the README.MD). From what I can see - so far - is, that only a single operation should be performed with the CUPS API at any given time. So maybe a global mutex could provide enough guarding for the entire crate. I will look more into that or maybe you have already experience with this.
• optimizing the get_job_info operation, as right now it pulls all jobs from the server and iterates over them. This could become an issue with a large job history. But I am not sure CUPS offers a simpler way to do that.

Please feel free to chime in on those first observations.

[tillkamppeter]

@ronnybremer thanks a lot for observations and suggestions!

@ronnybremer "media" is the curremt way to go, "PageSize" is from the deprecated PPD files, and as PPD files will go away in CUPS 3.x, "PageSize" will go away, too.

@mintu, for the units you should support all units which CUPS supports. Most importantly, PWG is using 1/100 mm, PostScript uses 1/72 inch (aka "pt" or "points"), mm and cm should also be supported. As you are creating CUPS bindings here, you should use what the original libcups functions output and also provide libcups' APIs for unit conversion or for telling in which unit a function should do its output.

@ronnybremer To get margins, see appropriate IPP attributes. all IPP attributes can be polled from the printer. To set margins you create a "media-col", an IPP data structure containing the 2 size dimensions and 4 margins for the page.

@Gmin2 the CUPS API has functionality to set the user for an inquiry to CUPS, you should make this API also available in your Rust bindings.

@Gmin2 I do not really remember now whether libcups has also async API functions, but generally offering such functions to Rust developers by having them in this crate would be very useful.

Generally, for Rust programmers who want to get printing-related functionality into their apps the way to go is:

• Printing from desktop app -> create a print dialog using @TitikshaBansal's cpdb-rs crate instead of talking directly to CUPS
• Doing anything else, printer setup tool, job applet, ... (for example for the @system76 folks for the COSMIC desktop) use this crate

[ronnybremer]

Thank you @tillkamppeter for your comments and insights.

@ronnybremer "media" is the curremt way to go, "PageSize" is from the deprecated PPD files, and as PPD files will go away in CUPS 3.x, "PageSize" will go away, too.

Thank you, I will make that change in my code.

@ronnybremer To get margins, see appropriate IPP attributes. all IPP attributes can be polled from the printer. To set margins you create a "media-col", an IPP data structure containing the 2 size dimensions and 4 margins for the page.

Indeed, I am aware of that. However, to create a media-col you have to rely on IPP operation attributes, so no longer on CUPS lp options. I would need to dig deeper into the crate to find out how to pass those along for a print job.

@Gmin2 the CUPS API has functionality to set the user for an inquiry to CUPS, you should make this API also available in your Rust bindings.

[tillkamppeter]

@ronnybremer thanks for the suggestions.

The limited time of the GSoC project was used now to create Rust bindings for the libcups API, meaning resembling the API in Rust, so that one can use it from Rust apps. In the future the crate can get extended to add more convenience functions, for example to ease finding out what the margins are and set margins for printing a photo or text.

Fur just printing (no admin or job control) you can (and should) use @TitikshaBansal's CPDB API. It is more oriented to print a job and it allows your app not only to print via CUPS but also on cloud printing services if they provide a CPDB backend.

[tillkamppeter]

@mmstick @jyn514 WDYT?